Field of the Invention
This invention relates to a device for generating a virtual light image and includes a real light source, a retroreflector surface, and a semi-transparent mirror. The virtual light image of the real light source is produced in that light beams coming from the real light source are reflected on the surface of the semi-transparent mirror, then strike the surface of the retroreflector surface, and from there, through retroreflection, travel back to the semi-transparent mirror. The semi-transparent mirror allows a portion of these beams to pass through. The beams that the semi-transparent mirror allows to pass through then intersect essentially at a point. In this way, a suitably positioned observer perceives a (virtual) light source that appears to be positioned at this intersecting point.
Discussion of Related Art
Devices known from the prior art can implement the above-described concept.
PCT International Publication WO 82/00911 discloses a device for producing a virtual light source of the type mentioned at the beginning. Thus, the device uses the real light source, the retroreflector surface, and the semi-transparent mirror as described above. The retroreflector surface is embodied as flat and the semi-transparent mirror that is likewise embodied as flat is situated so that it is rotated by an angle of approximately 45 degrees relative to the retroreflector surface. The retroreflector surface in this case is situated so that the light of the real light source transmitted through the semi-transparent mirror does not reach the retroreflector surface.
European Patent Reference EP 0 460 873 A1 describes a device for producing a virtual light source by the real light source, the semi-transparent mirror, and two retroreflector surfaces. The retroreflector surfaces, which are embodied as flat, are arranged at right angles to each other. The semi-transparent mirror is placed between the retroreflector surfaces so that the two surfaces are positioned symmetrically with regard to the mirror.
German Patent Reference DE 10 2008 022 011 A1 describes another device for producing a virtual light image. The device in German Patent Reference DE 10 2008 022 011 A1 is characterized by the fact that the retroreflector surface and semi-transparent mirror are positioned parallel to each other.
PCT International Publication WO 83/03019 A1 discloses an embodiment of the device for producing the virtual light image, in which the retroreflector surface is embodied in the form of a sector of a cylinder. This embodiment has the disadvantage that the virtual light image is overlapped by the light of the real light source when an observer looks into the device from the front. In another embodiment in PCT International Publication WO 83/03019 A1, a retroreflector surface is curved in some regions and has perforations through which the light of the real light source situated behind it passes in the direction of the semi-transparent mirror. This embodiment in turn has the disadvantage of a poor light output, which results in a low intensity of the virtual light image.
Another device of the type mentioned at the beginning, with two retroreflector surfaces situated on both sides of a beam splitter is disclosed in German Patent Reference DE 691 08 609 T2.
The flat shape and the positioning of the retroreflector surface disclosed in the above-mentioned references have disadvantages that are primarily due to the properties of retroreflective materials.
The property of retroreflectors of reflecting incident light in the direction from which the light is coming is not ideal so that a given light beam is usually reflected as a light cone by the retroreflector surface. If the distance (optical distance) between a point on the retroreflector surface and the virtual light image is labeled D, then due to this non-ideal reflection, the sharpness of the image falls as D rises.
Furthermore, retroreflection is direction-dependent. If A is the angle (incidence angle) between the normal at a given point on the retroreflector surface and the incident light beam, where the angle A also corresponds to the angle (reflection angle) between the normal and the axis of the reflected light cone, then the opening angle of the light cone increases as A increases. This results in blurriness and a reduction in the brightness of the light image.
The use of a non-adapted retroreflector surface inevitably results in the occurrence of the deteriorations in above-mentioned image.
In particular, the arrangement of the retroreflector surface at an angle of 45 degrees relative to the semi-transparent mirror is also disadvantageous with regard to the size of the visibility range.